With development of a mobile communications system, higher quality of a service provided by the communications system is achieved. To maintain a long-term competitive advantage of the 3GPP (the 3rd generation partnership project, the 3rd Generation Partnership Project), standard formulation work for LTE-A (LTE-advanced, Long Term Evolution Advanced) as further evolution of an LTE (long term evolution, Long Term Evolution) technology is in progress. To further improve spectral efficiency of the communications system and data throughput of a user, a carrier aggregation (CA, carrier aggregation) technology is introduced into LTE-A. Carrier aggregation enables a user equipment (user equipment, UE) to perform uplink and downlink communication by using multiple component carriers (CC, component carrier) at the same time, so as to implement high-speed data transmission.
The carrier aggregation of an LTE system may roughly be divided into carrier aggregation for cells inside a base station and carrier aggregation for cells between base stations. The carrier aggregation for cells inside a base station is controlled only by one base station, and therefore is relatively easy to implement. The carrier aggregation for cells between base stations may further be divided into carrier aggregation for cells between macro base stations and carrier aggregation for cells between a macro base station and a home base station. The carrier aggregation for cells between macro base stations can improve a data throughput of a user in an edge area of a base station, so as to improve user perception. In addition to improving a data throughput of a user, the carrier aggregation for cells between a macro base station and a home base station can further offload system traffic from a macro network, and compared with a network with home base stations only, can further reduce occurrence of handovers.
During the high-speed data transmission performed by using the carrier aggregation for cells between base stations, when handover occurs on a base station that carries data, it is difficult for an existing data transmission method based on carrier aggregation to achieve accuracy and continuity of data transmission, which causes a data loss when the handover occurs, and therefore reduces use perception of a user.